Grain mineral quality of dryland legumes as affected by elevated CO2 and drought: a FACE study on lentil (Lens culinaris) and faba bean (Vicia faba)

Stimulation of grain yield under elevated [CO2] grown plants is often associated with the deterioration of grain quality. This effect may be further complicated by the frequent occurrence of drought, as predicted in most of the climate change scenarios. Lentil (Lens culinaris Medik.) and faba bean (Vicia faba L.) were grown in the Australian Grains Free Air CO2 Enrichment facility under either ambient CO2 concentration ([CO2], ~400 µmol mol–1) or elevated [CO2] (e[CO2], ~550 µmol mol–1), and with two contrasting watering regimes (for faba bean) or over two consecutive seasons contrasting in rainfall (for lentil), to investigate the interactive effect of e[CO2] and drought on concentrations of selected grain minerals (Fe, Zn, Ca, Mg, P, K, S, Cu, Mn, Na). Grain mineral concentration (Fe, Zn, Ca, K, S, Cu) increased and grain mineral yield (i.e. g mineral per plot surface area) decreased in dry growing environments, and vice versa in wet growing environments. Elevated [CO2] decreased Fe, Zn, P and S concentrations in both crops; however, the relative decrease was greater under dry (20–25%) than wet (4–10%) growing conditions. Principal component analysis showed that greater grain yield stimulation under e[CO2] was associated with a reduction in Fe and Zn concentrations, indicating a yield dilution effect, but this was not consistently observed for other minerals. Even if energy intake is kept constant to adjust for lower yields, decreased legume micronutrients densities under e[CO2] may have negative consequences for human nutrition, especially under drier conditions and in areas with less access to food.